Embodiments of the invention are directed to systems, apparatuses, and devices used to convert an input electrical signal into sound, and more specifically, to an electro-acoustic transducer that may be used in an earpiece, headphone, loudspeaker or similar device. Embodiments of the invention utilize a driver that causes the motion of one or more airfoil-shaped elements in order to generate sound in a more efficient manner than conventional devices.
In many devices and systems it is desirable to generate sound in response to an input signal. This process is commonly performed using an electro-acoustic transducer which functions to convert an input electrical signal into acoustic or sound waves which are then perceived by a listener. Some form of such a transducer may be found in earpieces, headphones, and loudspeakers, to name a few examples. A variety of electro-acoustic transducers are known, with their operation typically being based on controlling the motion of an element in response to an input signal, where the motion of the element creates an acoustic wave. The acoustic wave created is a longitudinal wave that is generated by a local pressure gradient that results from the motion of the element. For example, a common electro-acoustic transducer such as a loudspeaker operates by moving a diaphragm (which is typically cone-shaped) approximately longitudinally in order to generate longitudinal sound waves propagating in the same direction as the movement of the diaphragm or cone. The diaphragm or cone may be driven (i.e., caused to move) by a solenoid or other form of electromagnetic driver, by a piezoelectric driver, etc. An electrical signal is input to the driver to produce the motion of the diaphragm, with the signal typically produced by a signal source (such as an amplifier, tuner, MP3 decoder, etc.). As the signal changes, the motion of the diaphragm changes in response, with the diaphragm motion generating the desired acoustic waves which are perceived as sounds by a listener.
Although such electro-acoustic transduction devices and methods of operation perform the desired function, a problem common to many such transduction devices is their relatively low efficiency with regards to the conversion of electrical energy into sound energy (for example, typically only a small percentage of the input electrical energy is converted into sound). This inefficiency leads to a number of disadvantages for many existing speaker designs, primarily because they must use more electrical power to generate a given sound level. For example, this inherent inefficiency can impact the size of a power source that is needed to obtain a desired level of operation (such as a battery for a portable loudspeaker), as well as the cost of the electrical energy required for operation, and its storage or transmission equipment. This inefficiency also means that the driver mechanism for a transducer must be relatively stronger, typically leading to a larger, more expensive, and heavier system as a whole. In general, many common speaker designs tend to be more expensive, have greater power consumption, and be larger and heavier than would be optimal, with these disadvantages being at least partially due to the inefficiency of the electrical-to-acoustic conversion process.
As recognized by the inventor, a key contributor to the inefficiency of the electrical to acoustic energy conversion process in many transducers is the relative (in)efficiency of the conversion of mechanical energy of the moving part of a transducer (e.g., the cone or the diaphragm) into sound waves. This is at least partially the result of a relatively poor match between the acoustic impedance of the diaphragm (or other moving parts) and the surrounding air, as the optimum efficiency of a transducer is expected to occur when the impedance of such elements are substantially equal. In the case of a typical loudspeaker, air (in common with many gases) has a relatively low acoustic impedance, whereas a diaphragm or cone (being substantially solid) has a significantly higher acoustic impedance.
While such an inefficiency is a problem for many uses of electro-acoustic transducers, it can be a particularly significant problem in the production of lower sound frequencies (for example bass frequencies). At such frequencies, the loudspeaker or transducer is typically small compared to the wavelength of sound being produced, often resulting in poor reproduction of those frequencies. Using a physically larger speaker may provide a solution, but at the cost of increased weight and power consumption, which are both undesirable for some types of systems (such as portable sound reproduction systems).
As a result of these problems, and as recognized by the inventor of the invention described herein, an electro-acoustic transducer that provided an increased loudspeaker efficiency, particularly with regards to the efficiency of the conversion of the mechanical energy of a moving part of the transducer into sound energy, would be desirable. Such a design would potentially have the benefits of reducing the cost, size, power consumption and weight of loudspeakers and other systems employing acoustic transducers.
What is desired is an electro-acoustic transducer that is capable of more efficiently converting electrical energy into acoustic energy than presently available designs. Embodiments of the invention address these problems and other problems individually and collectively.